1. Field of the Invention
The present invention relates to an optical recording medium. More particularly, the present invention relates to an optical recording medium including three or more recording layers.
2. Description of the Related Art
An optical recording medium such as CD (compact disc) or DVD (digital versatile disc) is widely used as a recording medium for storing digital data. As that optical recording medium, a multilayer optical recording medium is known that includes a plurality of information recording layers in order to increase storage capacity. The recording layers are stacked with light transmitting spacer layers interposed therebetween in the multilayer optical recording medium.
When a recording mark on one recording layer is reproduced in the aforementioned multilayer optical recording medium, a recording mark on another recording layer is not reproduced. However, if there is reflected light from the other recording layer and the amount of the reflected light or a distance between the recording layers is varied for some reason, the variation (hereinafter, crosstalk variation) may be superimposed as a noise on a reproduction signal.
In order to reduce an effect of interlayer crosstalk as described above, an optical recording medium is proposed in which distances between recording layers are intentionally made different, as described in Japanese Patent Laid-Open No. 2004-213720, for example.